Engine driven welding power supplies may be driven either by a DC generator or an AC generator (also called an alternator-rectifier). An AC generator generally includes, in addition to an alternator, a reactor followed by rectifiers to provide a DC output. AC driven welding power supplies are, generally, constant current type machines and the output volt-ampere characteristic of an AC driven welding power supply typically has a very steep slope. That is, the output current is nearly constant over a varying range of output voltage. Some welding processes are well suited for such an output. Other processes are not as well suited to a CC output, and are best performed with a set of output V-A curves having a single open circuit output voltage, then having a sloping characteristic down to a predetermined voltage level, then having a vertical characteristic (i.e., constant current) over a range of output voltages, and then again having a sloping characteristic to provide high output current for short circuit (i.e., tight arc) conditions.
One prior art generator driven welding power supply that can be used for a variety of processes is described in U.S. Pat. No. 5,734,147, entitled Method And Apparatus For Electronically Controlling The Output Of A Generator Driven Welding Power Supply, issued to Bunker et al., on Mar. 31, 1998, and is owned by the owner of this invention. U.S. Pat. No. 5,734,147 is hereby incorporated by reference, and discloses a power supply having output characteristics (also known as volt-ampere or V-A curves) that are shaped by simultaneously monitoring the output current of the welding supply and the generator output voltage and then controlling the generator field current based on the monitored information in conjunction with control reference inputs. In addition to shaping the V-A curves, the monitor and control circuits determine the transient response of the welding power supply which permits the output current to change rapidly in response to output voltage changes. This feature provides the user with more accurate control of the welding arc current. The monitor and control circuits also provide a constant, stable open circuit output voltage that provides a consistent characteristic for igniting the welding arc. Further, the monitor and control circuits compensate and stabilize the welding power supply during short circuit conditions. The controller may shape the output curves to emulate a DC generator, for example by causing the welding output V-A curves to have multiple breakpoints, and/or a substantially preset slope over a welding range wherein the preset slope does not vary over the output current range of the power supply. Also, the slope of the V-A output curve below the welding range may be different than the slope in the welding range.
Many generator driven welding power supplies provide a 110 VAC, 240 VAC, 480 VAC, single or three phase, auxiliary power output. Such power sources are used for hand tools, lights, etc. Because the devices powered by the auxiliary power are designed to operate using line current, it is desirable to provide a "flat" V-A curve, i.e., a constant voltage, regardless of the current draw. This is in direct contrast to the output desirable for many welding application. Accordingly, it is desirable to provide a generator driven welding power supply that provides a droop in the welding output, but a flat auxiliary output.
U.S. Pat. No. 5,734,147 taught to use a generator that inherently provides a CV output (for a given RPM) so the auxiliary voltage was generally CV. Then, the welding output is controlled using electronic field control to be CC (or whatever shape desired). Additionally, the auxiliary voltage is controlled using a frequency to voltage converter providing an output indicative of engine speed. A welding regulator uses the f-v output to control an auxiliary voltage. Assuming the auxiliary voltage is proportional to the engine RPM, the proper auxiliary voltage is obtained. While this system is better than other prior art systems, it does not provide for closed loop control of the auxiliary voltage. When the welding output is active, a closed loop auxiliary voltage control may not be desirable, as it could adversely affect the welding output control. However, when the welding output is not active, a closed loop auxiliary voltage control could be used, and would likely be more accurate than prior art open loop controls.
Another problem with auxiliary output is that when the auxiliary power demand suddenly increases, and the engine is in idle, it could cause the engine to stall.
Accordingly, an engine driven welding power supply with a closed loop control of auxiliary voltage, when the welding output is inactive, is desired. Preferably, such a control would utilize electronic field control, and would build on the weld output control, so as to avoid unnecessary expense and complication. Also, such a system would preferably include an auxiliary power controller that delayed or inhibited full power when the engine is idling, so as to reduce the likelihood of a stall.